Copier and sheet stripping finger therefor

ABSTRACT

A copier having a rotatable drum includes one or more stripping fingers to detach the leading edge of a copy sheet from the drum and one or more wheels arranged to be struck by the leading edge and to prevent subsequent contact between the stripping fingers and the copy sheet as the copy sheet is advanced from the drum along a forwarding path.

United States Patent [191 Mihalik et a1.

1 Nov. 11, 1975 154] COPIER AND SHEET STRIPPING FINGER THEREFOR [75] Inventors: Nandor Mihalik,

Walton-on-Thames; Nicholas Gilbert Shreeve, Weybridge. both of England [73] Assignee: Gestetner Byfleet Limited, London,

England [22 Filed: Feb.2l, 1974 211 App1.No.:444,372

[30] Foreign Application Priority Data Feb. 23. 1973 United Kingdom 9050/73 [52] US. Cl. 271/174;- 271/D1G. 2 [51] Int. Cl. B65H 29/56 [58] Field of Search 27l/D1G. 2, 80, 174

[56] References Cited UNITED STATES PATENTS 1.011.046 12/1911 Freeman 271/80 1.078.238 11/1913 Barber .t 271/80 1.737.616 12/1929 Saatman 271/D1G. 2

2.844.372 7/1958 Liebenow et a1. 271/80 3.642.274 2/1972 Herrington et a1. 271/81) Primary EXUHI/Ile'fF-RlChard A. SChaCher Assistant E.\'uminerRobert Saifer Attorney, Agent, or FirlnFleit & Jacobson 1 57] ABSTRACT A copier having a rotatable drum includes one or more stripping fingers to detach the leading edge of a copy sheet from thedrum and one or more wheels arranged to be struck by the leading edge and to prevent subsequent contact between the stripping fingers and the copy sheet as the copy sheet is advanced from the drum along a forwarding path.

13 Claims. 3 Drawing Figures U.S. Patent Nov. 11, 1975 Sheet 1 of2 3,918,702

FIG].

U.S. Patent -Ndv. 11,1975 Sheet20f2 3,918,702

COPIER AND SHEET STRIPPING FINGER THEREFOR The present invention relates to a device for separating a copy sheet from a drum, for example the charged drum of an electrostatographic copying machine.

The image on a drum is is transferred to copy sheets which tend to cling to the drum by electrostatic attraction and various means have been proposed for effecting the efficient peeling or stripping of copy sheets from such drums. The chief problem to be overcome is to effect this stripping or peeling without scratching the surface of the drum and the undeveloped toner deposited on the surface of the sheet.

Various solutions to this have been proposed, notably that of providing mechanical stripping fingers located very closely adjacent the drum surfaceHowever this solution suffers from the disadvantages that in sliding past the edge presented by a finger, the image on the surface of a copy sheet tends to become disturbed, which may give rise to unsightly lengthwiselines.

According to one aspect of the present invention there is provided a copier having a drum on which, in use of the copier, copy sheets are carried and from which they are advanced along a forwarding path; and a stripper assembly for removing copy sheets from said drum, the assembly including at least one stripping finger and at least one freely rotatable wheel, the or each stripping finger having a stripping tip urged into contact with the peripheral surface of the drum to detach the leading edge of a copy sheet from the periphery of the drum, the or each wheel having a narrow peripheral rim and being located in the forwarding path and immediately downstream of theor each stripping tip and having an axis of rotation substantially perpendicular to the direction of feed of the copy sheet and substantially parallel to the axis of rotation of the drum, the or each wheel and the or each stripping finger being positioned relative to the drum, such that the drum and the or each wheel share a common tangential plane towards which any point of the drum surface moves during its approach to a stripping finger and toone side of which the drum and the or each wheel both lie, the or each stripping finger being shaped and positioned to lie entirely on one side of said common. tangential plane. Preferably two stripping fingers are provided positioned such that one stripping finger engages the copy sheet immediately inwardly of each of the lateral edges of the copy sheet. It has also been found to be particularly convenient to mount each wheel on an associated stripping finger, for example on a shaft extending from a lateral surface of the associated stripping finger.

The configuration of the periphery of the wheels may conform to any one of a large variety of patterns, but is advantageously such that the instantaneous contact area between a wheel and the surface of'the copy sheet is always small enough to ensure that no substsantial marks are left on the surface of the sheet to mark the image after printing. Thus, such a wheel may suitably have a discontinuous periphery of undulating form, for example, it may be knurled or fluted in an axial direc- 'tion.

According to a second aspect of the present invention there is provided a stripping finger assembly for peeling sheets from a drum in a copying machine, such finger having a tip at one end and carrying a freely rotatable wheel provided with a narrow rim which projects beyond the edge of the finger which, in use of the finger is intended to be the lower edge at a position near to, but spaced rearwardly from the tip.

In order that the invention be more clearly understood, the following description will be given, merely by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a fragmentary elevation of a preferred embodiment of stripping finger and wheel according to the invention,

FIG. 2 is a plan view of the stripping finger and wheel of FIG. 1, and

FIG. 3 is a section on the line 3-3 of FIG. 2.

In FIG. I, an image bearing drum rotates about its axis 28 in the direction of the arrow A. and on its peripheral surface 2 a copy sheet (not shown) rides towards a stripping tip 6 having a blunt forward end of a stripping finger 4 which carries a wheel 10. Stripping finger 4 is pivotally mounted on a shaft 16 which passes through the finger at the end opposite the stripping tip 6 and the pivotal stripping finger assembly is biased in the anticlockwise sense by means of a counter weight 20. Thus the stripping tip 6 is urged against the peripheral surface 2 of the drum. Other suitable biasing means such as spring biasing may instead be used if desired,

In FIG. 1 it can be seen that the pivot axis 16 of the stripping finger 4 is substantially parallel to the axis 28 of the drum.

The biasing force on the stripping tip 6 is preferably of the order of 1 gram.

The wheel 10 is freely rotatably supported by a boss 8 extending transversely of the longitudinal axis of the stripping finger 4 substantially parallel to the axis of the drum and is shown as having a serrated peripheral edge comprising teeth 14, The wheel tapers towards that edge when viewed in the plan view of FIG. 2. The edge may equally be knurled in the axial direction and/or fluted inthe peripheral direction. By so tapering or fluting the actual cross section and ensuring that the rolling edge is of undulating form so as to consist of a succession of points it is possible to minimise the area of contact between the wheel and the as yet unfused image on the surface of the copy sheet being stripped.

When the leading edge of a copy sheet (not shown) carried on the peripheral surface 2 of the drum comes into contact with the stripping tip 6, the leading edge of the copy sheet becomes detached from the peripheral surface 2 and moves down the concave under surface 12 of the stripping finger towards the wheel 10. This wheel 10 is positioned such that when the leading edge of the copy sheet has advanced a small distance, it comes into rolling contact with the peripheral edge of the wheel 10, and thereafter the remainder of the copy sheet does not contact stripping finger 4 during subsequent motion of the copy sheet. This effect is aided by the concavely undercut lower surface 12 of the stripping finger 4.

Once the copy sheet has come into rolling contact with the peripheral edge of wheel 10, the frictional force between drum and that portion of the copy sheet remaining on the peripheral surface 2 of the drum causes the copy sheet to continue rolling over the wheel 10 and detaching itself from the peripheral surface 2 as the leading edge of the copy sheet moves towards and along the guides 26 forming a forwarding path.

FIG. 1 also shows certain geomctrical restraints on the relative positioning of the drum. stripping finger 4 and wheel to ensure correct operation of the invention. The dashed line 2224 represents a plane which is tangential to both the wheel 10 and the drum such that during clockwise rotation of the drum any point of the peripheral surface 2 of the drum moves from this tangential plane as it approaches the stripping tip 6 and such that both the drum and wheel 10 are located to one side of the tangential plane 22-24.

For the invention to operate the stripping tip 6 must be located to the same side of and spaced from that tangential plane as are the wheel 10 and the drum, as shown.

When a copy sheet from the peripheral surface f the drum comes into rolling contact with the wheel 10..

its path between them will approximately lie in the tangential plane defined above, although of course. some slight bowing of the sheet towards the stripping tip 6 will occur. The curvature of this bowing will depend on the flexibility of the copy sheet. The spacing of the stripping tip 6 from the tangential plane may suitably be chosen to ensure that no contact between stripping tip,6 and the bowed portion of the copy sheet occurs after the sheet has come into rolling contact with wheel 10.

ln the plan view of FIG. 2, the top surface of stripping tip' 6 is fluted. The lateral and lower surfaces of the finger 4 are shaped to define a longitudinally extending rib which tapers downwardly towards the concave under surface 12 and extends right up to the end of stripping tip 6 to ensure that the contact area between the strip-' ping finger 4 and the peripheral surface 2 of the drum or the image bearing surface of a copy sheet is always minimised, and to ensure that equally the stripping tip 6 does not scratch the delicate photoeonductor surface of the drum 1 or disturb the electrostatic image on the sheet.

It has been found that by utilising the combination of wheel and stripping finger according to the invention, the incidence of unsightly marks on the image bearing surfaces of copy sheets caused by scratching of the drum or copy sheet is markedly lower than with hitherto known copy sheet detaching means. This improvement is particularly noticeable with the finger and wheel shown in'FlGS. l to 3.

The stripping fingers themselves may be made of any suitable material.

We claim:

1. A copier including a drum rotatable in one direction about an axis and having a peripheral surface and means for carrying a copy sheet on said peripheral surface; means defining a forwarding path for copy sheets from said drum; stripping finger means positioned adjacent'said drum; stripping tip means of said stripping finger means positioned in contact with said drum; means biasing said stripping tip means against said peripheral surface of the drum; wheel means; shaft means carried by said stripping finger means and mounting said wheel means for rotation about an axis parallel to the axis of rotation of said drum and located immediately downstream of said stripping tip means in the direction of the sheet movement along said forwarding path; said drum and said wheel means sharing a common tangential plane from which any point on the drum surface moves during its approach to said stripping tip means, and to one side of which the drum and wheel means both lie,

said stripping finger means being shaped and positioned to lie entirely to said one side of said common; tangential plane. the stripping tip means being spaced 1 from saidtangential plane.

2. A copier as set forth in claim 1, wherein said stripping finger means and said wheel means consistof two stripping fingers and two wheels respectively, the stripping fingers being spaced in a direction parallel to said drum axis. and each wheel being located adjacent are spective one of said stripping fingers.

3. A copier as set forth in claim 1, wherein said wheel means have contoured circumferential surface means, i

of undulating form. I y y 4. A copier as set forth in claim 1, wherein the stripping finger means have means defining a concavely un- I dercut lower surface.

5. A copier as set forth'in claim 1, and including 1 means mounting the stripping finger means for pivoting about an axis substantially parallel to the axis of the drum; and wherein said stripping tip biasing means means comprise means for gravity biasing said finger for pivoting movement about said axis.

6. A copier as set forth in claim 1, wherein said biasing means exerta biasing force on said tip means of the order of] gram.

7. A copier as set forth in claim 1, wherein said stripping tip means includes planar surface means extending in a plane parallel to said drum axis, and an edge to said '1 planar surface means said edge being blunt when viewed along a direction perpendicular to said plane.

8. A copier including a drum rotatable in one direction about an axis and having a peripheral surface and means for carrying a copy sheet on said peripheral surface; means defining a forwarding path for copy sheets on said drum; stripping finger means positioned adjacent said drum; stripping tip means of said strippingfinger means positioned in contact with said drum; means biasing said stripping tip means against said peripheral surface of the drum; wheel means; radially outer edges for said wheel means, the wheel means having an axial cross-section which tapers towards said outer edges; and means mounting said wheel means for rotation about an axis parallel to the axis of rotation of said drum and located immediately downstream of said I stripping tip means in the direction of copy sheet movement along said forwarding path; said drum and said wheel means sharing a common tangential plane. from which any point from the drum surface moves during its approach to said stripping tip means, and to one side of which the drum and wheel means both lie, said stripping finger means being shaped and positioned to lie entirely to one side of said common tangential plane,

and the stripping tip means being spaced from said. tangential plane.

9. A copier including a drum rotatable in one direction about a horizontal axis and having a peripheral surface and means for carrying a copy sheet on said pe-:

ripheral surface; means defining a forwarding path forl copy sheets from said drum; stripping finger means positioned adjacent said drum below a horizontal plane including said axis; stripping tip means of said stripping finger means positioned in contact with said drum;

wheel means for rotation about an axis parallel to said axis of rotation of said drum and located immediately downstream of said stripping tip means in the direction of copy sheet movement along said forwarding path; said drum and said wheel means sharing a common tangential plane from which any point from the drum surface moves during its approach to said stripping tip means, said drum and wheel means both lying to one side of said tangential plane; said stripping finger means being shaped and positioned to lie entirely to one side of said common tangential plane, and the stripping tip means being spaced from said tangential plane.

10. A copier as set forth in claim 9, wherein said wheel means have contoured circumferential surface means of undulating form.

11. A copier as set forth in claim 9, wherein the stripping finger means have means defining a concavely undercut lower surface.

12. A copier as set forthvin claim 9, and including means mounting the stripping finger means for pivoting about an axis substantially parallel to the axis of the drum; and wherein said stripping tip biasing means comprise means for gravity biasing said finger means for pivoting movement about said axis.

13. A copier as set forth in claim 9, wherein said stripping tip means includes upwardly facing planar surface means extending in a plane parallel to said drum axis; and an edge to said planar surface means. said edge being blunt when viewed in a direction perpendicular to said plane and said downwardly projecting rib being shaped to taper towards and to terminate at said edge. 

1. A copier including a drum rotatable in one direction about an axis and having a peripheral surface and means for carrying a copy sheet on said peripheral surface; means defining a forwarding path for copy sheets from said drum; stripping finger means positioned adjacent said drum; stripping tip means of said stripping finger means positioned in contact with said drum; means biasing said stripping tip means against said peripheral surface of the drum; wheel means; shaft means carried by said stripping finger means and mounting said wheel means for rotation about an axis parallel to the axis of rotation of said drum and located immediately downstream of said stripping tip means in the direction of the sheet movement along said forwarding path; said drum and said wheel means sharing a common tangential plane from which any point on the drum surface moves during its approach to said stripping tip means, and to one side of which the drum and wheel means both lie, said stripping finger means being shaped and positioned to lie entirely to said one side of said common tangential plane, the stripping tip means being spaced from said tangential plane.
 2. A copier as set forth in claim 1, wherein said stripping finger means and said wheel means consist of two stripping fingers and two wheels respectively, the stripping fingers being spaced in a direction parallel to said drum axis, and each wheel being located adjacent a respective one of said stripping fingers.
 3. A copier as set forth in claim 1, wherein said wheel means have contoured circumferential surface means of undulating form.
 4. A copier as set forth in claim 1, wherein the stripping finger means have means defining a concavely undercut lower surface.
 5. A copier as set forth in claim 1, and including means mounting the stripping finger means for pivoting about an axis subStantially parallel to the axis of the drum; and wherein said stripping tip biasing means comprise means for gravity biasing said finger means for pivoting movement about said axis.
 6. A copier as set forth in claim 1, wherein said biasing means exert a biasing force on said tip means of the order of 1 gram.
 7. A copier as set forth in claim 1, wherein said stripping tip means includes planar surface means extending in a plane parallel to said drum axis, and an edge to said planar surface means said edge being blunt when viewed along a direction perpendicular to said plane.
 8. A copier including a drum rotatable in one direction about an axis and having a peripheral surface and means for carrying a copy sheet on said peripheral surface; means defining a forwarding path for copy sheets on said drum; stripping finger means positioned adjacent said drum; stripping tip means of said stripping finger means positioned in contact with said drum; means biasing said stripping tip means against said peripheral surface of the drum; wheel means; radially outer edges for said wheel means, the wheel means having an axial cross-section which tapers towards said outer edges; and means mounting said wheel means for rotation about an axis parallel to the axis of rotation of said drum and located immediately downstream of said stripping tip means in the direction of copy sheet movement along said forwarding path; said drum and said wheel means sharing a common tangential plane from which any point from the drum surface moves during its approach to said stripping tip means, and to one side of which the drum and wheel means both lie, said stripping finger means being shaped and positioned to lie entirely to one side of said common tangential plane, and the stripping tip means being spaced from said tangential plane.
 9. A copier including a drum rotatable in one direction about a horizontal axis and having a peripheral surface and means for carrying a copy sheet on said peripheral surface; means defining a forwarding path for copy sheets from said drum; stripping finger means positioned adjacent said drum below a horizontal plane including said axis; stripping tip means of said stripping finger means positioned in contact with said drum; means defining a longitudinally extending rib projecting downwardly from said finger means and tapering towards said stripping tip means; means biasing said stripping tip means against said peripheral surface of the drum; wheel means; and means mounting said wheel means for rotation about an axis parallel to said axis of rotation of said drum and located immediately downstream of said stripping tip means in the direction of copy sheet movement along said forwarding path; said drum and said wheel means sharing a common tangential plane from which any point from the drum surface moves during its approach to said stripping tip means, said drum and wheel means both lying to one side of said tangential plane; said stripping finger means being shaped and positioned to lie entirely to one side of said common tangential plane, and the stripping tip means being spaced from said tangential plane.
 10. A copier as set forth in claim 9, wherein said wheel means have contoured circumferential surface means of undulating form.
 11. A copier as set forth in claim 9, wherein the stripping finger means have means defining a concavely undercut lower surface.
 12. A copier as set forth in claim 9, and including means mounting the stripping finger means for pivoting about an axis substantially parallel to the axis of the drum; and wherein said stripping tip biasing means comprise means for gravity biasing said finger means for pivoting movement about said axis.
 13. A copier as set forth in claim 9, wherein said stripping tip means includes upwardly facing planar surface means extending in a plane parallel to said drum axis; and an edge to said planar surface means, said edge being blunt when viewed in a direction perpendicular to said Plane and said downwardly projecting rib being shaped to taper towards and to terminate at said edge. 